in this video we're going to talk about enzymes so what are enzymes enzymes at least most of them are protein-based catalysts that speed up chemical reactions and the way they speed up chemical reactions is by lowering the activation energy so let's draw an energy diagram we have energy on the y-axis the reaction coordinate on the x-axis in blue this would be the uncatalyzed reaction so this is the energy of the reactants the products and the difference between the energy of the transition state and the reactants is the activation energy now in red i'm going to show the energy diagram with the use of a catalyst so the energy of the reactants and products will be the same but notice that the energy of the transition state is a lot less so as you can see with the catalyzed reaction in red the activation energy has been decreased and that's how enzymes speed up chemical reactions now most enzymes are protein-based catalysts but there are some enzymes that are not made up of proteins and these are rna catalysts known as ribozymes now let's get rid of this picture it's very easy to identify an enzyme if you're given its name enzymes they have the suffix ace for instance sucrase is an enzyme that breaks down sucrose into fructose and glucose so here's the overall reaction this is sucrose and then with the enzyme sucrase this will speed up the chemical breakdown of sucrose into glucose and fructose now enzymes have an active site with a unique three-dimensional shape that is specific for the substrate that it binds with so let's use this reaction as an example so this will be the enzyme and this is going to be the substrate which is sucrose sucrose is a disaccharide it's made up of two sugar units glucose and fructose so i'm going to write e for enzyme s for substrate as you can see the active site of the enzyme which is right here it has a unique shape that is complementary to the substrate now there's two types of models that you need to be familiar with the lock and key model and the induced fit model the basic idea of the lock and key model is that the substrate fits exactly with the active side of the enzyme just as a key fits exactly into the lock activating the door so that it opens but the induced fit model there's a little bit more to it with the induced fit model as the substrate enters the active site the shape of the enzyme changes slightly so that it fits even better with the substrate so it changes slightly such that it becomes even more complementary to the shape of the the substrate so that's the idea of the induced fit model the enzyme enhances its shape so that it fits better with the substrate now let's get rid of this i'm always running out of space here so once the enzyme combines with the substrate we're going to get something called an enzyme substrate complex abbreviated es so this is when the enzyme is catalyzed in the reaction in this case the breakdown of sucrose and then once it finishes doing its job it's going to return back to its original shape and then the products will be released so we have g for glucose f for fructose so we have the original enzyme and these are the products so as you can see the enzyme is a catalyst that is not used up in a reaction so if we were to write the overall reaction of this so it's going to be s plus e and then that's going to turn into es the enzyme substrate complex that's the intermediate for this reaction and then it's going to be e plus p where p is the products so notice that the enzyme appears in the beginning of the reaction and at the end of the reaction so the enzyme is not used up in the chemical reaction it can be reused to react with another sucrose molecule converting that into glucose and fructose so make sure you understand that enzymes they speed up chemical reactions but they're not consumed in the reaction now let's move on to the next point the factors that affect enzyme activity so the first one is the ph enzymes have an optimal ph upon which they work most enzymes their optimal ph is somewhere between six and eight because your body has a ph between six and eight the optimal ph will be the x value that occurs at this point so in this example that would be somewhere around seven on the y-axis we have the rate so at this point the enzyme it's working at its best at its highest rate now some enzymes they have an optimal ph that is not around seven for instance the enzyme pepsin has an optimal ph somewhere between two and three because it exists in your stomach under acidic conditions another factor that affects enzyme activity is temperature and like ph there's a graph that corresponds to that so we have temperature on the x-axis and the rate of the reaction on the y-axis now the graph will look something like this so there is an optimal temperature at which the rate is at its maximum so below that increasing the temperature will increase the rate of the enzyme activity that is the left side because as you increase the temperature along the x-axis you can see the rate is going up now once you go past that optimal spot or that optimal temperature as you can see the rate of the reaction quickly decreases at certain temperatures or rather at certain high temperatures proteins can be denatured they can lose their shape and thus they can lose their ability to function and so if the temperature is too high the enzyme is not going to work as well as it should because of denaturation so that's something to keep in mind so proteins their shape is dependent on the temperature and the ph another factor that affects the enzyme activity is the concentration as you increase the concentration of the substrate or the enzyme the rate of the reaction will increase as well up to a limit if the concentration is too high once you reach that optimal rate of reaction increase in the concentration won't work anymore so let me give you a graph to help you visualize this so we're going to have the rate of the reaction on the y-axis and the concentration on the x-axis let's use c as to say to represent the concentration of the substrate so initially as you increase the concentration of the substrate by moving to the right the rate of the reaction will increase now eventually it's going to level off so at this point this is true increasing the concentration of the substrate or the enzyme the rate is going up now once you reach that optimal rate of the reaction which is probably going to be somewhere just above that red line once you get close to it increasing the concentration has negligible effect on the rate of the reaction as you can see the rate is not changing much so this is true up to a certain limit now another factor that affects enzyme activity are the presence of inhibitors and activators inhibitors are substances that inhibit the activity of an enzyme so it slows it down so let me draw an enzyme so there goes my enzyme and let's draw a similar substrate that we had before now there's two types of inhibitors that you need to be familiar with competitive inhibitors which i'm going to draw in green so this would be the competitive inhibitor this inhibitor wants to bind at the active site of the substrate so if it gets there it's going to block the substrate from entering that site so let's put that there so that will be an example of a competitive inhibitor if it bonds to the active site the substrate can't get in and so it prevents the substrate from interacting with the enzyme so that's why they're competitive inhibitors the inhibitor competes with the substrate for the same active site now another type of inhibitor is a non-competitive inhibitor which i'm going to put in green so this non-competitive inhibitor which is also like an allosteric inhibitor it binds to the allosteric site of the enzyme so the allosteric site is somewhere away from the active site which is here i'm going to write a s for active site so once that non-competitive inhibitor or allosteric inhibitor bonds to that site the enzyme changes shape such that it no longer fits with the substrate so let me go back to my terrible drawing skills so now the substrate can't bond with this enzyme because it no longer fits with the enzyme so that's how a non-competitive inhibitor could decrease enzyme activity with this substrate an activator is basically the opposite of an inhibitor an activator would be something that would activate the enzyme towards the substrate so those are some factors that affect enzyme activity in addition some enzymes require cofactors and coenzymes to function cofactors include inorganic metal ions such as the zinc 2 plus cation and coenzymes include organic molecules such as vitamins as you continue to study biology or even biochemistry you're going to encounter some complicated chemical reactions and if you could understand the name of the enzyme that catalyzed that reaction then you can understand what's happening in the reaction the first enzyme that we're going to talk about is protease so this is an enzyme that breaks down proteins and polypeptides into amino acids the second one that we're going to briefly review is lipase so ace tells you that it's an enzyme the root word lipe or lipid tells you dealing with lipids and fats lipase is an enzyme that breaks down fats such as triglycerides into glycerol and fatty acids another example is isomerase so the root word isomer this is an enzyme that catalyzes rearrangement reactions it can convert a compound into its isomer number four transferase so this is an enzyme that is going to transfer something it transfers a functional group from one molecule to another the next one is kinase so this enzyme transfers a phosphate group particularly from atp to another molecule number six dehydrogenase so let's think about this word hydrogen and the word d so this is an enzyme that removes hydrogen atoms from a molecule next amylase think of starches such as amylosin amylopectin well starch plant starch is composed of for the most part 20 amylose and 80 amylopectin if i remember it correctly but amylase is an enzyme that breaks down starch into simple sugars like glucose number eight oxido reductase so think of the word oxidation and reduction so we're dealing with redox reactions in a redox reaction there's a transfer of electrons in an oxidation reaction electrons are lost but in a reduction reaction a substance picks up or gains electrons so oxidoreductase is an enzyme that catalyzes the transfer of electrons from one molecule to another number nine is hydrolase so think of the word hydrolysis used in water to split a big molecule into two smaller components so hydro excuse me hydrolase is an enzyme that catalyzes hydrolysis reactions so those are some enzymes that you may want to familiarize yourself with